Desizing effluents

Type of size BODs mg Oj/kg Oxygen consumption kg O, per 1000 kg of textile material 

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Poly(vinyl alcohol) can be recovered from the desizing Hquid by means of commercial ultrafiltration equipment. Recovery rates and effluent losses ate inversely proportional to the PVA solution viscosity and independent of the degree of hydrolysis. 

Clearly, it is the exoenzymes that are of interest in textile processing, an area which has seen considerable development in recent years. Originally used only in the preparatory processes of scouring and desizing, they are now also used to modify textile surfaces in finishing as well as in effluent treatment. 

This removal of size residues inevitably raises environmental questions. Unfortunately, the various size polymers and their associated additives respond to different methods of removal. It is therefore highly desirable to know which sizes and other components have been used in a given case so that appropriate methods of removal can be formulated. This is not always easy, particularly in commission dyehouses or printworks where sizing has been carried out elsewhere. Analytical procedures are available but these require appropriate facilities and expertise. Once desizing has been carried out there arises the question of how to dispose of the effluent. 

Desizing of m = 1000 kg of goods, which contain 5% of weight starch size p = 0.05) cause a load Lcod = 50 kg and Lbod = 30 kg. Using 10 L of water for desizing of 1 kg of fabric, a total volume of 10,000 L will be required and the load Lcod = 50 kg will be diluted in this volume. As a result, a COD value of 5000 mg/L can be calculated for the effluent. 

The UF membranes are protected from yarn fibers by a vibrating screen filter and 20 to 50 n cartridge filters. This makes possible the use of spiral wound modules which have a life of 24 to 30 months. The desizer waste effluent usually contains between 0.5 and 1.5% PVA. The UF concentrates this PVA up to 10% for direct use in the slasher. This final concentration is monitored and automatically controlled by an in-line refractometer. A small amount of desizer waste is purged to drain to prevent the buildup of low MW solutes. 

Desizing Acidic, oxidative, enzymatic depending on type of size Sizes and size residues in effluent, impact on COD, BOD... 

Stegmaier T, Trauer J, Wunderlich W (1998), Reducing effluent loading in sizing and desizing , MelliandIntern., 1, 38-42. 

The textile industry requires large amounts of water, energy, and auxiliary chemicals [147]. The search for environmental-friendly methods has lead to the utilization of enzymes. Several enzymes have been used in textile processes in order to achieve improved and fashionable fabric properties. Among other enzymes for textile processing, amylases (used for desizing), cellulases (denim finishing), laccase (decolourization of textile effluents and textile bleaching) are commercially available [148, 149]. 

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